Project Summary This application proposes to test the cellular properties and functionality of a calcium quantum dot (qdot)- fluorescence energy transfer (FRET) sensor we have developed. These probes have been designed with the intent to provide fast, high spatial resolution fluorescence reporting of calcium signaling in cells in acute experimental conditions, within an immediate four to six hour window. There are a number of efficient genetically encoded calcium indicators that exist, but the time required for expression (typically several days) precludes their use in acute experiments like the ones we are targeting. Organic dye calcium indicators can be bulk loaded into cells with relatively short incubation periods but suffer from broad emission spectra, which prevents the detection of multiple signals due to the spectral overlap, significant photobleaching to even short exposures, and have limited spatial resolution. Here we propose testing a novel fast loading acute calcium indicator with robust and improved optical properties. We anticipate similar needs from other investigators and believe the probes we are developing will be of significant widespread value and utility. Specifically, in this application we will investigate physical dispersion and distribution of our quantum dot- FRET probes under biological conditions and use the probes to image calcium signaling in astrocyte neural glial cells.